The present invention relates to integrated circuits. In particular, the present invention relates to input/output buffer architecture for integrated circuits.
Integrated circuits are typically formed by depositing and diffusing material into a silicon substrate to form an integrated circuit die. Connections are made to circuit elements within the integrated circuit through bond pads located on the surface of the die. In the past, these bond pads have commonly been located around the perimeter of the die to facilitate connecting the bond pads to a package through a wire bonding process that connects one end of a fine gold or aluminum wire to the bond pad and a second end to the package.
Within an integrated circuit, each bond pad is connected to an input buffer or an output buffer. Input buffers typically include receivers that change the logic levels to be compatible with the requirements of the circuits which comprise the majority of the integrated circuit. Output buffers include drivers that amplify the drive capability in order to efficiently pass output signals from the integrated circuit to a remote location. Typically, the input/output buffers use larger circuit elements than those found on the remainder of the integrated circuit die.
Each buffer, both input and output, also includes an electrostatic discharge region connected directly to the bond pad to protect the integrated circuit from an electrostatic discharge at the bond pad. If a large electrical charge reaches the bond pad, the electrostatic discharge region directs the charge through a network of circuit elements designed to minimize heat generation and over-voltage stress.
In recent years, different techniques have been developed for bonding the integrated circuit die to the package. One technique, known as flip-chip bonding, applies solder bumps to the bond pads and then flips the entire die onto the package. Once the chip is flipped, the solder bumps are heated so that they reflow, making connections between the bond pads and the contacts of the package.
Flip-chip technology has been proposed for use in full-area-array technology where bump pads are not only present at the perimeter of the die, but are present across the entire surface of the die. However, such full-area-array technology has not resulted in large performance gains because the buffers attached to the bump pads, in general, remain at the perimeter of the die. The buffers have not moved to the core of the integrated circuit, where the bump pads are located, because the different sized electronics of the buffer make it difficult to integrate the buffer electronics with the core electronics of the integrated circuit. Specifically, the large size of the buffer electronics and the layout sensitivity of the electrostatic discharge circuitry make it difficult to position the buffer within the core electronics.